We had the same issue this past weekend with our 2012 16BH. When I turned the water heater on I could hear the igniter clicking, it would pause for a few moments and the clicking would start again. That's when the propane built up in the heater tube would finally ignite and sound like someone hit the rear of the trailer.
After turning the propane off and waiting a few minutes, I opened the cover of the heater, and took out 3 sheet metal screws for the covers over the burner.
The first thing I noticed was the rusty spots around the mounting plate for the igniter. I took the 1 screw holding the igniter in place and removed the igniter carefully so as not to bend either prong of the igniter. Using sandpaper I cleaned the mounting areas and the surface of the igniter holder of any rust buildup and then reassembled.
I turned the propane back on and the heater lit instantly for the rest of the trip. Tried it again last night at home and again it lit at once. The igniter gets it's ground to the "-" prong from these metal brackets. I am going to disassemble it again this weekend and make sure that all areas are still clean, then paint this area with a hi-temp paint to maybe help retard the rust problem.
Hope this helps someone.